1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic process, such as a copying machine, a printer, or a facsimile.
2. Description of the Related Art
In a developing unit installed in an electrophotographic image forming apparatus, when the temperature of a developer is raised due to stirring of the developer, the charging characteristics of the developer may be deteriorated to cause an image failure such as reduction in image density. Further, when temperature around a photosensitive body is raised due to friction between the photosensitive body and a photosensitive body cleaner, there is also a problem of causing toner to melt and attach to the photosensitive body. Therefore, the developer is cooled or the discharge of toner is controlled to reduce the deterioration of the developer, and cooling is performed around the photosensitive body to suppress the temperature rise of the photosensitive body.
In such a case, however, there is another problem that the running cost increases due to noise and waste of energy caused by the cooling operation, and excess discharge of toner.
Therefore, a temperature sensor is conventionally provided in the developing unit to control the cooling operation in order to balance energy saving and noise reduction with cooling (Japanese Patent Application Laid-Open No. 2009-217067 (Patent Document 1)).
However, like in the developing unit disclosed in Patent Document 1, in a case where a temperature sensor is provided in a developing unit, the temperature of a developing unit can be measured but the temperature of a photosensitive body and temperature around the photosensitive body cannot be measured. Therefore, there is a need to add another temperature sensor.
Especially, like a tandem color image forming apparatus, in a system having a mode such as a K-monochrome (black monochrome) mode where there is an image forming section in which the developing unit is not driven but only the photosensitive body rotates, a difference in temperature between the developing unit and the photosensitive body becomes great. This makes it difficult for the temperature sensor in the developing unit to measure the temperature of the photosensitive body.